title: Clinical pharmacokinetics of phenytoin in the dog: a reevaluation.
abstract: The pharmacokinetics of phenytoin, as well as drug plasma concentrations, during continued treatment were studied in the dog. After IV injection of 10 mg/kg, the average elimination half-life was 4.4 hours, which is in good agreement with previous studies. Bioavailability from tablet formulation was rather poor (av 36% compared with that obtained with IV) and showed great variation between dogs. Even with the dosage regimen of 20 mg of drug/kg given TID orally, therapeutic plasma concentrations could only be maintained for the first 2 or 3 days of treatment; these subsequently decreased to ineffective concentrations during the 1st week of treatment. This effect was accompanied by considerable reductions in half-life, indicating that phenytoin is a strong inducer of microsomal drug metabolism in the dog. Phenytoin must be considered as poorly suited for the treatment of canine epilepsy.
mesh_terms: D000284:Administration, Oral; D000818:Animals; D001682:Biological Availability; D004285:Dogs / Q000097:blood / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004830:Epilepsy, Tonic-Clonic / Q000188:drug therapy / Q000662:veterinary*; D005069:Evaluation Studies as Topic; D005260:Female; D006207:Half-Life; D007275:Injections, Intravenous; D007700:Kinetics; D008297:Male; D010672:Phenytoin / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*
chemical_list: D010672:Phenytoin